<!DOCTYPE HTML>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>定时器</title>
    <script type="text/javascript">
        var attime;

        function clock() {
            var time = new Date();
            attime = time.toString("HH:mm:ss");

            document.getElementById("clock").value = attime;
        }

        setInterval("clock()", 1000);
        var a = 123;
        var b = "123";
        alert(a + b);
        var str = "11" + 2 - "1";
        document.write(str);
        document.write(typeof str);

    </script>
</head>
<body>
<form>
    <input type="text" id="clock" size="50"/>
</form>
</body>
</html>